Stent delivery system

ABSTRACT

A stent delivery system includes a catheter with an axially extending inner core and outer sheath. Axially spaced rings extending from a relatively narrow diameter portion of the inner core proximate the distal end thereof. The rings engage proximal portions of a compacted stent disposed within the sheath and over the core and rings. A proximal handle of the system has a first portion that supports the sheath and a second portion that supports the core for relative displacement of the core and the sheath. Retraction of the sheath relative to the core uncovers the stent engaged by the rings which tends to remain stationary relative to the core so that upon partial retraction of the sheath a distal end of the stent expands to its expanded form. Further retraction of the sheath deploys the stent, retracting the core returns the distal portion of the stent into the sheath.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation application of co-pending U.S. patent applicationSer. No. 08/873,484, filed Jun. 12, 1997, which is a continuationapplication of U.S. patent application Ser. No. 08/526,968, filed Sep.12, 1995, now U.S. Pat. No. 5,702,418, both of which are incorporatedherein by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a percutaneous and endoscopic delivery of astent in a patient's body and more particularly to a stent deliverysystem including a catheter for the selective deployment of anexpandable stent.

2. Description of Related Art

Stents are well known endoprostheses. A typical endoprosthetic stentcomprises a tubular structure that expands radially from a compact formfor transit to an expanded form for implantation. Radial expansioncauses the stent to implant into the tissues of a wall of a “vessel”being repaired or bridged to maintain its patency. Such stents may beutilized in body canals, blood vessels, ducts and other body passages,and the term “vessel” is meant to include all such passages.

Stents can be characterized as self-expansive and mechanicallyexpansive. This invention relates to both self-expansive andmechanically expansive stents further characterized by being formed of asingle wire or plurality of wires woven together to form a meshstructure which can be located on or in a distal end of a tubular body,such as a medical catheter, in such compact form. A delivery system forsuch stent comprises a catheter with various associated controlapparatus extending from a distal end to a proximal end. Such a deliverysystem enables a surgeon to guide the distal end with the compact stentto a selected location in a patient's vessel. The surgeon then operatesthe control apparatus to release and expand the stent so as to deployand fix the stent in the selected location. The control apparatus may beintegral with the catheter for a mechanically expandable stent orancillary to the catheter for a self-expansive stent. In either version,the control apparatus releases the stent from the catheter and, in thecase of a mechanically expansive stent, expands the stent radially.After the stent has expanded, the surgeon returns the catheter typicallyto its pre-deployment form, free from the stent, and then removes thecatheter from the patient. The expanded stent remains in the vessel inits expanded shape to maintain vessel patency.

Stent delivery systems must generally conform to several importantcriteria. First, it is critical in most applications to keep thetransverse dimension of the delivery system to a minimum, as the distalend of the delivery system typically must be navigated through and alonga patient's lumens either in a percantaneous insertion procedure orthrough the working channel of an endoscope. Second, the delivery systemmust facilitate the deployment of the stent into contact with thepatient's vessel walls once it is located at a selected site. Third, thestent delivery system must easily disengage from the stent afterdeployment to enable separation of the delivery system from the deployedstent. Fourth, the procedure for removing the delivery system from thebody must be straightforward and relatively simple to speed and ease thework of a physician employing the stent delivery system. Fifth, thestent delivery system must be reliable and efficient to reduce traumaand patient risk. Sixth, preferably the delivery system should alsoenable partial deployment and retraction of the stent to enable thesurgeon to recover a stent not properly positioned during deploymentthereof.

The prior art stent delivery systems for self-expansive endoprostheticstents are illustrated by the following United States Letters Patent:

-   -   U.S. Pat. No. 4,580,568 (1986) Gianturco    -   U.S. Pat. No. 4,655,771 (1987) Wallsten    -   U.S. Pat. No. 4,681,110 (1987) Wiktor    -   U.S. Pat. No. 4,732,152 (1988) Wallsten et al.    -   U.S. Pat. No. 5,026,377 (1991) Burton et al.

U.S. Pat. No. 4,580,568 to Gianturco discloses a system for delivering aself-expanding stent. The system comprises a tubular sheath positionedwith a distal end proximate a selected delivery site. The stent is thencompressed and inserted into a proximal end of the sheath. A userinserts a pusher rod into the tubular sheath and urges the stent throughthe sheath to a position proximate the distal end of the tubular member.The user then retracts the sheath relative to the push rod to releasethe stent.

U.S. Pat. No. 4,655,771 to Wallsten discloses a delivery system for astent that includes a catheter that supports a tubular stent in acompact form on its exterior distal end surface. Gripper membersproximate the proximal and distal ends of the tubular stent secure tothe catheter. A handle at the proximal end of the tubular part of theapparatus enables a user to control the axial movement of the grippermembers. That is, axial displacement of the gripper members by thecontrol mechanisms frees the stent from the outer surface of thecatheter and enables expansion of the stent.

U.S. Pat. No. 4,681,110 to Wiktor discloses a catheter arrangement inwhich a tubular member contains a radially expandable liner and adeployment mechanism for deploying the liner. The deployment mechanismincludes an internal tube that extends through the outer portion of thetube and engages a proximal end of the liner. Distal displacement of theinner tube relative to the outer tube urges the liner distally of thedistal end of the outer tube enables the liner to deploy in its radiallyexpanded form.

U.S. Pat. No. 4,732,152 to Wallsten et al. discloses a device and methodfor implantation of a prosthetic stent. The stent is maintained in acompact state within the device during transport to a selected locationwithin a patient's vessels and then is released to expand and fix in apatient's vessel.

The following United States Letters Patent illustrate prior art stentdelivery systems for mechanically expansive stents:

-   -   U.S. Pat. No. 4,553,545 (1985) Maass et al.    -   U.S. Pat. No. 4,733,665 (1988) Palmaz    -   U.S. Pat. No. 4,907,336 (1990) Gianturco    -   U.S. Pat. No. 4,950,227 (1990) Savin et al.    -   U.S. Pat. No. 5,026,377 (1991) Burton et al.

U.S. Pat. No. 4,553,545 to Maass et al. discloses a coil spring stentand an instrument for transporting the stent in a compact form and thendeploying the stent in an expanded form within a patient's body. Atubular body carried on the distal end of a catheter underlies andsupports the stent. Proximal and distal ends of the stent are clampedbetween the ends of the tubular body and enlarged first and second endsections of the catheter. The end sections connect by first and secondportions of a coaxial cable to a knob member at a proximal end of theinstrument. A second knob member at the proximal end connects with thetubular body so that relative rotation of the knobs in a first senseurges rotation of the tubular body relative to the end section to urgeradial expansion of the stent thereby. Opposite rotation of the knobstend to contract the stent. Successive opposed relative axialdisplacement of the knobs successively widens the space between thefirst and second end sections respectively and the tubular body tothereby release the stent from the tubular member.

U.S. Pat. No. 4,733,665 to Palmaz and U.S. Pat. No. 4,907,336 toGianturco disclose a stent delivery system with a mesh and wire stentrespectively, mounted on an expandable balloon at a distal end of thecatheter. A surgeon positions the distal end of the catheter in apatient's vessel and expands the balloon and stent into contact with thevessel wall. Then the surgeon deflates the balloon and removes thecatheter.

In U.S. Pat. No. 4,950,227 to Savin et al. a stent is placed at a distalend of a catheter surrounding an expandable balloon. Proximal and distalends of the stent underlie flaps on the outer surface of the catheter.Expansion of the balloon releases the stent from the flaps and expandsthe stent into its operative expanded form.

In U.S. Pat. No. 5,026,377 to Burton et al. an outer sheath overlies astent carried in a compact form at the extreme distal end of thecatheter. An elongated gripping member supported by an inner corefrictionally grips the stent in its compact form. Manipulation of aproximal handle member selectively retracts the sheath to expose theself-expanding stent and enables deployment at the select location. Atan intermediate position a physician can selectively retract the innercore to retract the stent within the outer sheath.

Burton et al. do provide apparatus that enables a surgeon to retract astent after displacement has begun. However, Burton et al. do notprovide any indication that the stent has deployed beyond a point atwhich retraction is no longer possible. That is, Burton et al. fail todisclose apparatus enabling a surgeon to determine when the axial forcesnecessary to reduce the expanded portion of the stent have exceeded thefrictional bond between the stent and a gripping surface that retainsthe stent on the catheter. Furthermore, in the prior art, such as thatdisclosed by Burton et al., the stent in its compact form is closelyproximate both a core and an outer sheath. The inner stent surface bearson the core and the outer stent surface bears on the inner sheathsurface to thereby form a frictional engagement therebetween. This alsoreduces the overall flexibility of the distal end of the stent deliverysystem. Maneuvering a distal end of reduced flexibility through thetortious paths often encountered in a patient's vessels can increasepatient trauma and can, in some cases, make this treatment modalityimpracticable. Thus, a surgeon frequently faces the decision of riskingadditional trauma to the patient or adopting another procedure fortreating the patient. Thus, none of these prior art delivery systems andmethods enable the delivery of a stent to a selected location ofpatient's body and facilitate the retraction of a partially deployedstent, that provides reasonable flexibility of the distal end forpositioning the stent at the selected location and that provides to aphysician a defined zone of retractability of the stent.

SUMMARY

Therefore, it is an object of this invention to provide a method andsystem for either percantaneous or endoscopic delivery of a stent at aselected location in a vessel of a patient.

It is another object of this invention to provide a stent deliverysystem with a flexible distal end adapted for passage through thevessels of a patient and with the capability of selective deployment andretraction of the stent.

It is still another object of this invention to provide a stent deliverysystem with capability of selective deployment and retraction of thestent characterized by a flexible distal end for use in percantaneousand endoscopic procedures and adapted for passage through tortious pathsdefined by the vessels of a patient.

It is yet another object of this invention to provide a method andsystem for delivery of a stent which reduces the steps and timenecessary to deliver a stent to a selected location of a vessel in apatient.

It is yet still another object of this invention to provide a method andsystem for delivery of a stent which enables a user to ascertain whetherthe stent is retractable.

It is a further object of this invention to provide a method and systemfor delivery of a stent which is relatively simple and inexpensive toproduce and use.

In accordance with one aspect of this invention a delivery system forpositioning a stent in a patient's vessel includes a catheter forpositioning the stent at a predetermined position in the patient's body.The catheter includes a sheath normally overlying the stent in itscompact form and an inner core normally underlying the stent in itscompact transport form. Two spaced rings extend radially from the innercore and engage the stent in its compact form to enable deployment ofthe stent by distal displacement thereof relative to the sheath andretraction of the stent within the sheath by proximal displacementthereof relative to the sheath.

According to another aspect of this invention a delivery system includesa distal end having a flexible sheath and a flexible core at a distalend of the system for overlying and underlying, respectively, aself-expansible stent positionable in a compact form. The stent issupported on at least two spaced rings secured to the core. Retractingthe sheath relative to the core deploys the stent; retraction of thecore relative to the sheath prior to full deployment of the stentretracts the stent relative to the sheath.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims particularly point out and distinctly claim thesubject matter of this invention. The various objects, advantages andnovel features of this invention will be more fully apparent from areading of the following detailed description in conjunction with theaccompanying drawings in which like reference numerals refer to likeparts, and in which:

FIG. 1 is a plan view in partial cross-section illustrating anembodiment of a stent delivery system according to this invention;

FIG. 2 is an enlarged view of a distal end of the embodiment of FIG. 1;

FIG. 3 is a sectional view taken along the line 3-3 in FIG. 2;

FIG. 4 is a plan view of the embodiment of FIG. 1 with the stent in apartially deployed position;

FIG. 5 is a plan view of the embodiment of FIG. 1 with the stent in afully deployed position;

FIG. 6 is an enlarged plan view similar to FIG. 1 of another embodimentof this invention; and

FIG. 7 is a plan view similar to FIG. 1 of yet another embodiment ofthis invention particularly useful in deploying a non-self-expandingstent.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

A stent delivery system 10 according to this invention as depicted inFIG. 1 includes a elongated catheter 11 defined between a proximalhandle 12 and a distal end tip 13. An axially extending plastic core 14supports the distal end tip 13. The core 14 includes a relatively stiffportion 15 extending distally from the handle 12. A flexible thickportion 16 extends distally from the stiff portion 15. A flexible thindistal portion 17 extends between the portion 16 and the distal end tip13. The flexible thin portion 17 underlies a mesh stent 20 supported ina compacted form within the catheter 11 proximate the distal end tip 13for deployment from the catheter 11 in an expanded form within apatient's vessel 22.

First and second closely, but axially spaced rings 23 attach to the thinportion 17 to be intermediate the portion 17 and the stent 20 to engagethe stent 20. A slippery outer sheath 24, preferably formed of aradially flexible axially stiff material such as polytetrafluoroethyleneor other like material, overlies the stent 20 and extends proximally toa first handle portion 25. The stiff portion 15 of the core 14 securesto a second handle portion 26. The handle portions 25 and 26 aredisplaceable along the axis 27 relative to each other thereby to enableselective deployment and retraction of the stent 20.

In the embodiment of FIG. 1, the stiff portion 15 of the core 14, whichextends a substantial length of the catheter 11, is preferably formed ofa plastic material such as PEBAX® or an elongated coiled spring formedof plastic or metal such as Nitinol® which provides limited flexibilityso the catheter 11 can readily be pushed from the handle 12 through thepatient's vessel with little risk of kinking. The core portions 16 and17 are relatively flexible radially.

The presence of the stent 20 on the axially spaced rings 23 does notsignificantly retard the overall flexibility of the extreme distal endof the catheter 11, because the rings 23 which support the stent 20 aresubstantially spaced from the distal end tip 13. That is, the distalportion of the stent 20 floats in a radial sense over the core 17. Thusupon application of a radially directed force to the sheath 24 proximatethe distal end tip 13, the stent 20 tends to radially displace withinthe sheath 24 thereat. This feature eases the surgeon's task innavigating the catheter 11 through severely tortious paths oftenassociated with both endoscopic and percantaneous procedures. Thus,employment of this invention reduces the steps and time necessary fordelivery of a stent to a delivery site.

Once the system 10 is properly inserted, the distal end tip 13 will bepositioned at a selected location in a patient's vessel 22 fordeployment of the stent 20. This can be accomplished by various means,preferably by providing markers such as radiopaque rings or indicia 37on the core 17 proximate the distal end tip 15 to properly locate thesystem 10. Then a surgeon will operate the handle 12 to deploy the stent20.

As best seen in FIGS. 2 and 3, the stent 20 preferably comprises aplurality of interlocking loops 20A having spaced overlapping portions20B and single wire portions 20C intermediate thereof. The individualwires preferably have a diameter “D_(w)”, the rings 23 have an outerdiameter “D_(r)”, and the sheath 24 has an inner diameter “D_(s)”,wherein:4 D _(w) +D _(r) >D _(s)>2 D _(w) +D _(p)

Likewise the stent 20 when in its compact form has an outer diameterapproximately “D_(s)” and maximum inner diameter (ID_(max)) and minimuminner diameter (ID_(min)) where:ID _(max) ≈D _(s)−2 D _(w)andID _(min) ≈D _(s)−4 D _(w)

The outer diameter “D_(r)” of the rings 23 therefore is preferablybetween the maximum and minimum inner diameters of the stent 20 in itscompact form. Thus, as depicted in FIG. 1, the stent 20 is positionedwithin the sheath 24 with the single wire portions 20C overlying therings 23 and the overlapping portions 20B disposed between adjacentrings 23. Thus, upon distal displacement of the rings 23 distal faces ofthe rings 23 engage proximal surfaces of distally adjacent overlappingportions 20B to urge corresponding distal displacement of the stent 20.Likewise upon proximal displacement of the rings 23 proximal faces ofthe rings 23 engage distal surfaces of proximally adjacent overlappingportions 20B to urge corresponding proximal displacement of the stent20. As will now be appreciated the positive engagement between the stent20 and the rings 23 due to the interspersed portions of the stent havinglarge and small inner diameters, ID_(max) and ID_(min), enable theselective and relatively sure control of the surgeon in deploying andretracting the stent 20.

In the embodiment of this invention illustrated by FIG. 1, the surgeonpreferably grasps the handle portion 25 and the handle portion 26 withtwo hands, holds the handle portion 26 steady and retracts the handleportion 25. This retracts the sheath 24 relative to the core 14. Whenthe surgeon partially retracts the sheath to a position as shown in FIG.4, the distal portion of the stent 20 beyond the sheath expands. Thesurgeon can uses fluoroscopic or endoscopic viewing techniques andapparatus to determine whether the stent 20 is appropriately positioned.If the stent 20 is not properly positioned the surgeon displaces thehandle portion 26 proximally to retract the core 14, attached rings 23and the stent 20 fully within the sheath 24 so that the stent 20 anddelivery system returns to the condition as depicted in FIG. 1. Thedistal end can then be maneuvered to a desired location or into adesired orientation and the process repeated. Once the surgeon issatisfied with the location and orientation of the partially deployedstent 20, the surgeon merely fully retracts the handle 25 to fullydeploy the stent 20 as depicted in FIG. 5.

Those skilled in the art will now recognize that the ability to retracta partially deployed stent enables a surgeon to ascertain whether thestent 20 is properly positioned fluoroscopically and/or visually throughan endoscope before fully deploying the stent 20. This can be importantto both surgeon and patient as improper positioning can increase thetrauma and risk to a patient and curtail the efficiency of thetreatment. As is known, manipulation of handles at the proximal end of acatheter to deploy a stent often affects the site of deployment of thestent as the distal end of the catheter can be unintentionallytranslated by such manipulation. Likewise other factors, some of whichare only apparent upon deploying the stent can render a locationinitially thought to be inappropriate. For these reasons, the embodimentof FIG. 1 includes the indicia 37 thereon, so that a surgeon using afluoroscope or viewing channel of an endoscope can ascertain the extentof deployment of the stent 20, as more fully discussed below.

FIG. 6 depicts another embodiment of this invention. A single ring 23′mounts to the catheter. It has a slightly longer axial extension thaneach ring 23, but less than the axial distance between the interlockingloops 20A. The ring 23′ has an outer diameter (D_(r)′), that satisfiesthe conditions:D′ _(r)+4 D _(w) >D _(s) >D′ _(r)+2 D _(w)The operation and use of this embodiment is similarly identical to theembodiment of FIG. 1.

Referring now to FIG. 7, another delivery system 47 according to thisinvention includes the annular rings 23″ that support a stent 50 in acompact form. The stent 50, rather than being a self-expanding stent, isformed with a known material defining the mechanically expansible meshthat locks in an expanded form. The annular rings 23″ engage the stent50 in its compact form to enable retraction of the stent 50 byretraction of the handle portion 26 and to prevent retraction of thestent 50 when the sheath 24 is retracted by operation of the handle 25.In this embodiment, a balloon lumen (not shown) connects to anexpansible balloon 60 that underlies the stent 50 between proximal todistal ends 58 and 59. The balloon 60 also lies between the rings 23 andthe stent 50. If the sheath 24 is partially retracted to a positionsimilar to that of FIG. 2, inflating the balloon 60 expands only theexposed portion of the balloon 60 and the coextensive portion of thestent 50 that lies distally of the sheath 24.

If repositioning of the stent is required, the surgeon deflates theballoon 60 and retracts the core portion 17 to thereby contract thestent 50 to enable repositioning of the distal end of the system 47. Inthis embodiment an extreme distal end of the sheath 24 preferablyincludes an integral metal or hard plastic ring 61 to assist in thecompression of the stent 50 upon retraction thereof from is partiallydeployed condition. Once the stent 50 is partially deployed in asatisfactory position, the surgeon fully retracts the sheath 24 andfully inflate the balloon 60 to fully deploy the stent 50 thereat.

As previously indicated, the particular structures of the stent deliverysystems according to this invention are suited for use in proceduresusing either percantaneous or endoscopic insertion techniques. In anendoscopic insertion technique the surgeon inserts the catheter 11through the working channel 70 of an endoscopic device 71 (see FIG. 5).In either technique a central lumen such as lumen 30 in FIG. 4, canextend through the catheter 11 receive a guidewire 31. With the centrallumen 30, the surgeon can first position the guidewire 31 in the patientand then slide the catheter 11 over the guidewire 31 to position thecatheter 11 within the patient's vessels with relative ease.

In accordance with another aspect of this invention, the distal end tip13 can be formed of a radiopaque material or provided with a radiopaquemarker to improve fluoroscopic observation of the distal end of thesystems 10 and 47 of FIGS. 1 and 7. The core portion 17 and the extremedistal end 61 of the sheath 24 can also be provided with indicia 37 toindicate extension of the core 17 relative to the sheath. The indicia 37and 61 will generally be radiopaque indicia although in devicesaccording to this invention used with an endoscope 71 having a viewingchannel 73, the indicia 37 and 61 may be of a type only visuallyperceived (e.g. colored rings). Preferably the indicia 37 is arranged ina selected number; concentration and/or color to indicate when thedegree of deployment has reached a state where further distaldisplacement of the rings will render subsequent retraction of the stentimpossible. Thus, a surgeon upon observing the selected indicia 37 thatthe commitment to deploy or retract must be made.

Thus, the stent delivery system of this invention enables a surgeon toposition a compacted stent at a selected location and partially deploythe stent, then either fully deploy the stent or return the stent to itscompacted form. A surgeon after partially deploying a stent can, uponobserving a problem such as incorrect positioning or the like, retractthe stent within the sheath 24 and then reposition the distal end 13 ata selected location and commence deployment of the stent. The use of oneor more of the rings 23, 23′ or 23″ also tends to improve the radialflexibility of the distal end of the stent delivery systems according tothis invention as compared with such prior art systems. As should now beunderstood, the rings 23, 23′ and 23″ disclosed herein are structuresthat interlock with the stent when in its compact form. Thisinterlocking provides the improved control of the stent in deploying andretracting the stent relative to the catheter.

This invention has been disclosed in terms of certain embodiments. Itwill be apparent that many modifications can be made to the disclosedapparatus without departing from the invention. By way of example,additional rings to engage the stent may be employed, the rings or ringsused may included slots for receiving portions of the stent overlyingthe rings, and, in fact, a ring can be formed or defined by a pluralityof protuberances or fingers that extend from a core or similar structureto engage and interlock with portions of the stent with the minimuminner diameter. Therefore, it is the intent of the appended claims tocover all such variations and modifications as come within the truespirit and scope of this invention.

1. A stent delivery catheter comprising a core and a mesh stent, thecore having a plurality of protuberances extending therefrom, the meshstent overlaying the plurality of protuberances, each protuberance beingnonmovable relative to the core, the protuberances interlocking withportions of the mesh stent.
 2. The stent delivery catheter of claim 1wherein each of the plurality of protuberances form a ring.
 3. The stentof claim 1, the stent having a proximal end portion and a distal endportion, wherein only the proximal end portion of the stent overlays theplurality of protuberances.
 4. A stent delivery catheter comprising acore with a ring disposed thereabout and a stent disposed about thering, wherein the ring includes slots for receiving portions of thestent therein.
 5. The stent delivery catheter of claim 4 comprising aplurality of said ring.
 6. A stent delivery system comprising: acatheter and a stent, the catheter having a sheath and a core with atleast one ring extending radially therefrom, the core underlying thestent, the stent disposed about the ring, the sheath disposed about thestent and the core, wherein the stent is radially displaceable withinthe sheath.
 7. The stent of claim 6 comprising a plurality of said ring.8. The stent of claim 7 wherein two of said rings are located adjacentone another with a gap therebetween, the stent extending into said gap.9. The stent delivery system of claim 6, wherein the core islongitudinally moveable relative to the stent.
 10. A stent deliverysystem comprising: a catheter having a stent receiving region, the stentreceiving region includes at least two regions of a first fixed diameterand a region of a second fixed diameter different from said first fixeddiameter, the second fixed diameter being between adjacent regions offirst fixed diameter; a stent comprising a first portion and a secondportion, the first portion having a first inner diameter and the secondportion having a second inner diameter, the first inner diameter beingdifferent from the second inner diameter, wherein the stent overlays thestent receiving region so that the first portion of the stent overlays aregion of first fixed diameter and the second portion of the stentoverlays the region of second fixed diameter.
 11. The stent deliverycatheter of claim 10 comprising a plurality of regions of said secondfixed diameter.
 12. The stent delivery catheter of claim 10, the firstdiameter of the stent being greater than the second diameter of thestent and the first fixed diameter being greater than the second fixeddiameter.
 13. The stent delivery system of claim 6, the stent having alength, a plurality of proximal surfaces, and a plurality of distalsurfaces, the plurality of proximal surfaces and the plurality of distalsurfaces being distributed along the length of the stent, the at leastone ring having a proximal surface and a distal surface, wherein contactbetween the distal surface of the at least one ring with the proximalsurfaces of the stent moves the stent in a distal direction relative tothe sheath and contact between the proximal surface of the at least onering with the distal surface of the stent moves the stent in a proximaldirection relative to the sheath.
 14. The stent delivery catheter ofclaim 1, the mesh stent having a plurality of first portions with afirst inner diameter and a plurality of second portions with a secondinner diameter where the first inner diameter is greater than the secondinner diameter, one of the first portions overlaying one of theplurality of protuberances and one of the second portions being betweenthe two of the plurality of protuberances.